1. Field of Invention
The present invention relates to conductive paste, and particularly relates to conductive paste which has excellent conductivity or excellent electromagnetic-wave shielding properties.
2. Related Art
Recently, with the development of electronic equipment or the like, there have arisen problems such as the influence of electromagnetic waves generated from the electronic equipment or the like on human bodies, or the pollution of the environment caused by harmful substances such as solder or the like at the time of scrapping the electronic equipment or the like. In order to solve such problems, there have been developed electromagnetic wave shielding materials in which conductive fillers composed of metal, carbon, etc., are mixed into synthetic resin, or conductive paste which uses no lead.
For example, conductive paste in which copper-powder conductive fillers of atomized copper powder, electrolytic copper powder, or the like, are mixed into synthetic resin, is known well. In such conductive paste, a large quantity of conductive fillers must be mixed in order to obtain satisfactory electromagnetic wave shielding properties or satisfactory conductivity. Thus, there is a problem that the material cost is increased. In addition, such conductive paste becomes so heavy in weight that there is a problem that it is inferior in easiness in handling.
In consideration of the foregoing circumstances, it is an object of the present invention to provide conductive paste which is superior in electromagnetic wave shielding properties or conductivity in spite of the small loading of the conductive fillers.
In order to achieve the above object, according to the present invention, there is provided conductive paste wherein conductive fillers composed of copper micro-fibers are mixed into thermoplastic resin or thermosetting resin.
The conductive paste according to the present invention exhibits higher electric conductivity with a smaller loading of conductive fillers than conventional conductive paste in which copper powder conductive fillers of atomized copper powder, electrolytic copper powder, or the like, are mixed into synthetic resin. In addition, the conductive paste according to the present invention is also superior in electromagnetic wave shielding effect. The reason for this is guessed as follows. That is, conductive fillers obtained from copper micro-fibers have a fine fibrous form. Thus, the conductive fillers are dispersed into resin so as to be intertwined with one another. Therefore, the conductive fillers have many contact points with one another. Further, such a contact condition of the conductive fillers is kept so that a larger number of conductive paths than those in the conventional conductive paste are formed.